Ammoniated wet process phosphoric acid suspension base

ABSTRACT

An ammoniated wet process phosphoric acid suspension base is prepared by mixing wet process orthophosphoric acid and superphosphoric acid to provide a mixture containing about 10-20 percent polyphosphoric acid, and ammoniating the mixture to provide an N/P2O5 ratio of about 0.32-0.35 and thereafter cooling the material and seeding with finely divided diammonium phosphate crystals. Attapulgite clay may be added just before the seeding step.

O United States Patent 1 1 3,620,668

[72] Inventor Paul R. Cutter [56] References Cited 1 N sgg' UNITED STATES PATENTS [21] P 3,015,552 1/1962 Striplin etaL. 23/107 x [22] Filed May 17, 1968 3,057,711 10/1962 Reusser et al.. 23/107 X [451 Patented 1971 3 113 858 12/1963 Slack eta] 23/107 x [73] Assignee United States Steel Corporation mburgh h 3,199,973 8/1965 Moore 23/107X 3,077,381 2/1963 Ber teinson et al 23/165 D Primary Examiner-Oscar R. Vertiz Assistant Examiner-Charles B. Rodman Attorney-Gene Harsh [54] i g g g g PROCESS PHOSPHORIC ABSTRACT: An ammoniated wet process phosphoric acid C EN 0 BASE suspension base is prepared by mixing wet process 7 Cm No mm orthophosphoric acid and superphosphoric acid to provide a [52] U3, (L 23/107, mixture containing about 10-20 percent polyphosphoric acid, 71/33 and ammoniating the mixture to provide an N/P,O ratio of [51] In, ("1. C0"; 25/23 about 0.32-0.35 and thereafter cooling the material and seed- [50] Fieldofseardl 23/ 107; ing with finely divided diammonium phosphate crystals. At-

tapulgite clay may be added just before the seeding step.

AMMONIATED WET PROCESS PHOSPHORIC ACID SUSPENSION BASE BACKGROUND AND SUMMARY Wet process phosphoric acid contains a substantial percentage (usually l-5 percent) of metal (aluminum and iron) impurities which form metal phosphates during the preparation of a fertilizer and, since such phosphates are valuable, it is important to keep them in suspension during storage under varying weather conditions including freezing weather. A suspension base is prepared by ammoniating such wet process phosphoric acid, and it is important to have the ammoniated suspension base stable after long storage periods under weather conditions mentioned above so that the base can be employed at cold mix stations for forming different formulas by the addition of potassium chloride, urea, ammonium nitrate, etc.

It has been known that superphosphoric acid, by reason of its high content of polyphosphoric acid, is effective in sequestering metal impurities, but superphosphoric acid is difficult to manufacture and rather corrosive, and its cost per ton makes it unattractive economically in larger quantities than necessary as a source of the P When mixtures of superphosphoric acid and orthophosphoric acid are employed, it has been found that large monoammonium phosphate crystals grow very rapidly and are so troublesome that many manufacturers resort to the use of superphosphoric acid alone or a mixture in which the superphosphoric acid is by far the major portion of the mixture.

l have discovered that a mixture of wet process orthophosphoric acid and superphosphoric acid can be employed in which the polyphosphoric acid content is as little as -20 percent of the total P,O content, so that after ammoniation the N/P O, ratio is in the range of 0.32-0.35 so that the diammonium phosphate crystals dominate in the solid phase, leaving the monoammonium phosphate recessive, and by cooling the ammoniated material and seeding it with finely divided diammonium phosphate crystals, a suspension base is obtained which is substantially free of monoammonium phosphate crystals and which effectively suspends the metal phosphate during adverse temperature conditions. While not essential, i prefer to introduce a small amount of binder clay (preferably about 3 percent), such as, for example, attapulgite clay, into the ammoniated wet process phosphoric acid material after it has been cooled and prior to the seeding with diammonium phosphate crystals.

DETAILED DESCRIPTION In preparing the ammoniated wet process phosphoric acid suspension base, I mix a larger proportion of wet process orthophosphoric acid with a smaller proportion of superphosphoric acid to form a mixture in which the polyphosphoric acid content is from 8-80 percent by weight (preferably 10-20 percent by weight). Since the upper limit of polyphosphoric acid is not critical, one may use any desired amount of polyacid but, because of its expense, I wish to reduce the amount of polyacid employed and I find that generally about l0-20 percent of polyphosphoric acid is adequate.

By way of example, 80 percent by weight of wet process orthophosphoric acid may be mixed with about percent by weight of superphosphoric acid which contains about 50 percent polyphosphoric acids. Since the content of polyacids varies in the superphosphoric acid, the matter of mixing the acids to give the desired content of polyacid in the final mixture is a relatively simple proportioning procedure, and it is further a simple matter to ammoniate the mixture to bring the NIP- 0 ratio into the range of 0.32-0.35.

The ammoniation procedure is not critical but may be the conventional process in which ammonia and the phosphoric acid are heated and the temperatures then raised by the exothermic reaction. Usually the temperatures are in the range of about ISO-250 F. The desired end product is an ammonium phosphate having the N/l-BO, ratio of 0.32-0.35.

The ammoniated material is cooled below 200 F., and preferably to about F., and finely divided diammonium phosphate crystals are introduced into the mass. Usually about 0.1-2 percent of crystals by weight are added, and I prefer to use crystals which are extremely fine, passing a 325-mesh screen.

The resulting product is substantially free of the large monoammonium phosphate crystals and the metal impurities are effectively suspended in the base for substantial periods of time under cold weather conditions.

I have also found that it is advantageous to add a clay, such as attapulgite clay, in the suspension base after it is cooled below 200 F. and before the diammonium phosphate crystals are added. This also aids in stopping the growth of the monoammonium phosphate crystals, and aids also in the suspension of the metal phosphates. The mass should be strongly agitated during the addition of the clay.

In the foregoing operation, the high N/P,O, weight ratio gives maximum solubility and minimum crystal content, while at the same time this ratio encourages growth of diammonium phosphate over monoammonium phosphate. Cooperating with the high N/P,O ratio is the seeding with diammonium phosphate in encouraging the growth of diammonium phosphate while rendering monoammonium phosphate recessive. The process enables one to obtain a stable suspension with as low as l0-20 percent polyphosphoric acid in the suspension.

Specific examples which are illustrative of the invention may be set out as follows:

EXAMPLE I A l4--l4l4 suspension containing 14 percent by weight of each of N ,P,O and K 0 was prepared as follows. To begin with, a certain amount of water is placed in a container equipped with an agitator and an ammonia sparger. orthophosphoric acid derived from wet process methods and superphosphoric acid containing about 50 percent polyphosphoric acids are added to the water simultaneously with ammonia. About 75 percent of the 50,, is added to the suspension in the form of wet process, 54 percent P 0 acid and 25 percent from so-called superacid containing about 50 percent polyphosphates. Enough ammonia is added to the agitated container to maintain a pH of about 6.3; the reaction is continued until a specific gravity of about 1.40 is reached. At this point, a suspension base material is obtained having a nitrogen to P 0 composition ranging between 11-33-0 and 1236-0, or a N/Pp, weight ratio of 0.333. The suspension base is first cooled to about F. where 3 percent attapulgite clay is dusted into the suspension base while undergoing severe agitation. The base is then cooled to below 100' F. and 0.05 to 1 percent minus 325-mesh diammonium phosphate crystals are added to seed out a high number of uniformly sized crystals.

At this point, we have prepared what is called a suspension base which can be shipped by railroad car or tank truck to various so-called cold mix stations for completing the formula and distribution. The optimum suspension base as prepared above, with the proper ratio described and total concentration not exceeding 12-36-0, can be stored for a considerable length of'time and even under temperatures down to about 12 F. without any noticeable damage. To further prepare the l4l4-l4 formula, or finished grade, enough of thesuspension base is added to a cold mix tank to deliver 280 pounds of P 0 by means of the suspension base which contains 36 percent P 0 or 780 pounds of the base to make up one ton of product. The 780 pounds of base which contains 12 percent nitrogen means that 93.6 pounds of nitrogen have also been added to the cold mix formula. 186.4 pounds of nitrogen must still be needed to obtain the 14 percent N in the formula. For the remainder of the nitrogen, the normal procedure is to use a highly concentrated solution containing urea and ammonium nitrate to make up the difierence. If such a solution contains 32 percent nitrogen, then 585 pounds of the nitrogen solution would then be added to the mix tank. To place 280 pounds of K,O into the formula, 448 pounds of potassium chloride (in the crystal fonn) will then be needed. I have now 100 F.. 500 p.p.m. of -325-mesh diammonium phosphate crystals were added. After the addition of 2 percent clay, the temperature was lowered with minimum agitation and no air entrainment to about 100 F. and then the diammonium added 1,813 pounds to 1 ton of final product. Since the clay 5 p p a p y were added with air cmtainmem induce concentration has been reduced from 3 percent to about 1.2 'y l f percent, it usually is desireable to add about 0.5-1 percent while the F8 p f I p l clay at this point or about 10-20 pounds of attapulgite clay. I examples In considerable detail fondle purpose of illustrating now have room for about 165 pounds of minor nutrients and embPdlmems of 3 ""F It such M the m may demamt In the preparation f the fi al 10 detallsmay be vanedwidely by those sk11led 1n the art w1thout products from the optimum set of conditions previously outfrom the of my mvenuon' lined, the 14-14-14 represented a maximum total concentration of about 42. A final formula containing a higher per- A process for prepmuon i subdued amnfcfmated centage of active ingredients than 42 would probably be too wet f phosphonc acld suspension bases compmmg the thick for most applications and should best not be considered. followmgfteps Other formulas which were prepared at the mix stations are: addmg from about 8 to about so pengem 6 18 6 18 204040 1 l 3 perphosphoric acid to wet process orthophosphonc acid; 64 54644 etc 2. ammoniating the phosphoric acid mixture until the N/P,O,, ratio is from about 0.32 to about 0.35;

EXAMPLE I] 20 3. cooling the ammoniated mixture to below 200 F.; 4. seeding the ammoniated mixture with an effective Suspension ere prep d as des ribed in example I i h amount of finely divided diammonium phosphate the N/P,O, ratio above 0.32 percent, clay being omitted and crystals, the material seeded with finely divided diammonium 2. The process of claim 1 wherein the ammoniated mixture phosphate crystals, as shown in the following table. The same is seeded with from about 0.1 to about 2 weight percent of were stored under Florida winter storage conditions for 6 finely divided diammonium phosphate crystals. months and found to be satisfactory as indicated in the follow- 3. The process of claim 1 wherein the ammoniated mixture in table. is seeded with from about 0.1 to about 2 weight percent of TABLE I Compar- Percent P205 ison Percent Condltlons. Product dates pH Sp. gr. N Total Urtho loly N+P20s N/lzOs 6 months 3-PYRO-A 8/19/66 0. 0 1. 420 11. 05 35.04 33. 7s a. 7 46.60 0. 332 Satisfactory. 3% pyrophosphate 2/14/67 11. 49 34.60 32. 01s 4. x 46.09 0. s32

4-PYRO-A 8/20/66 6.0 1.410 11.53 35.88 33.00 0.0 47.58 0. 321 4% pyrophosphate 2/14/67 11.43 35.09 32.83 8.01 47.12 0. 320 Satisfactory. B-PYRO-A 8/22/66 6. 0 1.420 11.86 36.91 34. 73 6. (l 48. 77 0.321 5% pyrophosphate 2/14/67 12. 07 36. 68 34.10 s. 24 4s. 75 0. 320 Satisfactory.

. l flffi i .cmst l l EXAMPLE I]! diammonium phosphate crystals of 325 mesh size or smaller.

was out as dmfibed in exam k H 4. The process of claim 1 wherein from about 2 to about 3 P i y was added The tempempmn was weight percent of the total suspenslon base attapulgite clay is lowered m'below F and the cl 'ddcd t b0 t 170,]: added to the ammoniated phosphoric acid after cooling and Theclay was not y in $332 5 :5 but prior to seeding with finely divided diammonium phosphate crystals. m 3: g i z g z zgz a fl 5. The process of claim 1 wherein from about 10 to about 1 00' 1-" at zv hich time the finel divided diammonium weigh acid is add! p y I were added y process phosphoric acid.

P 6. The process of claim 1 wherein the ammoniated mixture EXAMPLE lv is cooled to below 100 F. prior to seeding with diammonium phosphate crystals.

The process was carried out as described in example 1 ex- 7. The product of the process of claim 1.

cept that after the ammoniated solution was lowered to about e e e e a 

2. The process of claim 1 wherein the ammoniated mixture is seeded with from about 0.1 to about 2 weight percent of finely divided diammonium phosphate crystals.
 2. ammoniating the phosphoric acid mixture until the N/P2O5 ratio is from about 0.32 to about 0.35;
 3. cooling the ammoniated mixture to below 200* F.; and
 3. The process of claim 1 wherein the ammoniated mixture is seeded with from about 0.1 to about 2 weight percent of diammonium phosphate crystals of 325 mesh size or smaller.
 4. The process of claim 1 wherein from about 2 to about 3 weight percent of the total suspension base attapulgite clay is added to the ammoniated phosphoric acid after cooling and prior to seeding with finely divided diammonium phosphate crystals.
 4. seeding the ammoniated mixture with an effective amount of finely divided diammonium phosphate crystals.
 5. The process of claim 1 wherein from about 10 to about 20 weight percent superphosphoric acid is added to the wet process phosphoric acid.
 6. The process of claim 1 wherein the ammoniated mixture is cooled to below 100* F. prior to seeding with diammonium phosphate crystals.
 7. The product of the process of claim
 1. 